Recombinomics: California and Texas Swine Flu Clusters Raise Concerns

Commentary

Recombinomics Commentary 07:03
April 24, 2009

Two of the new cases were among 16-year-olds at the same school in San Antonio "and there's a father-daughter pair in California," Schuchat said. The boy whose case was reported on Tuesday had flown to Dallas, but the CDC has found no links to the other Texas cases.

The above comments describe four of the five new swine flu cases (see updated map) recently confirmed by the CDC. The two high school students near San Antonio, Texas were friends and not linked to the San Diego case who flew to Dallas. Similarly there was no indication that the father daughter pair in San Diego Country were linked to the earlier cluster.

The two initial confirmed cases were also linked to clusters, but the relatives were not tested. However, it is almost certain that the two sets of contacts for the first two cases were also infected, creating four distinct clusters. The only individual case was the fifth new case, a female from Imperial County. Thus, of the 11 confirmed or suspect cases, only one was not in a cluster.

This clustering signals efficient transmission, but none of the cases have links to swine or the other clusters. The efficient transmission signals extensive silent transmission. As noted earlier, only two of the six initial cases were tested, and the testing was linked to a border surveillance program.

Thus, without the border surveillance, none if these cases would have been identified, with the possible exception of the hospitalized patient who was on a ventilator. However, the swine flu would have only been identified if the sample was sub-typed. The swine flu would test positive for influenza A, and treatment and symptoms would be the same for seasonal or swine flu.

Although all cases were in locations close to the Mexican border, no cases in Mexico have been confirmed. However, without the border surveillance no case in the United States would have been confirmed.

It is likely that there are swine flu cases in Mexico, and it is likely that the current influenza outbreak includes a high number of swine flu cases. There have been 20 fatalities due to atypical pneumonia, and cases have been unusually high for mid to late April. Samples have been sent to Canada for analysis, and the CDC said they were also investigating. However, there is little doubt that a high percentage of cases in Mexico are swine flu. School closings throughout southern Mexico, affecting millions of students were just announced.

As flu season ends in the northern hemisphere, identifying swine flu cases should be easier. However, the mild nature of the illness will likely lead to spread into the southern hemisphere increasing the frequency of co-infections with H1N1seasonal flu and acquisition of Tamiflu resistance (H274Y).

Aggressive testing of patients throughout the Americas is warranted, as well as testing in other areas.

The number of flu cases in Mexico, coupled with the high frequency of clusters in California and Texas, raises concerns that the swine flu will spread worldwide and expand into a major pandemic.

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